Process for the separation of n-paraf-



United States PatentQ 2,999,857 PROCESS FOR THE SEPARATION OF N-PARAF- FINS FROM HYDROCARBON OILS Alfred Hoppe, Frankfurt am Main, Germany, assignor to Edeleanu Gesellschaft m.b.H., Frankfurt am Main,

Germany, a body corporate of Germany N Drawing. Filed Oct. 3, 1958, Ser. No. 765,019

Claims priority, application Germany Oct. 10, 1957 6 Claims. (Cl. 260-965) This invention is concerned with the separation of n-parraflins from hydrocarbon oils.

The removal of straight-chain paraflins from mixtures of hydrocarbon by adduct formation with urea is known.

According to Serial Number 533,699 now abandoned there is provided a process for separating paraflim'c hydrocarbons or derivatives thereof from'hydrocarbon oils by treating the latter with an aqueous solution of urea in the presence of a solvent for the hydrocarbon oil wherein a solution of urea containing 1040% by weight of water is mixed with the oil to be treated and with an oil solvent of which the boiling point is within the temperature range desired for adduct formation, the mixture is brought to and maintained at the temperature desired for adduct formation by evaporating a part of the oil solvent while vigorously agitating the mixture, the granular adduct so formed is separated from the oil solution, the solvent is removed from the oil solution and the adduct decomposed into paraflinic hydrocarbons or derivatives thereof and urea solution. In carrying out this process it has been found that there is a tendency for the coarse agglomerate which precipitates out to contain unused urea.

Accordingly, in order to use up the urea in a more efficient manner, the agglomerate was broken up by intensive mixing with, for example, a turbine mixer. In this case, a sievable adduct was certainly obtained but, in spite of the fine division, free and unused urea may remain present. The breaking up of the adduct required a relatively long period of time and a considerable quantity of energy had to be expended for this pmpose.

The adduct formation is normally carried out under atmospheric pressure and the material which is to serve as a solvent for the oil suitably chosen. However, it is also known to carry out the adduct formation under pressures which lie above or below atmospheric pressure. In this case, the pressure is not altered during the adduct formation because the prevailing point of View is that this process cannot be influenced by an alteration of the pressure.

We have now found that a reduction of the pressure during the adduct formation is bound up with an unexpected technical result if the adduct formation is carried out according to specification No. 533,699.

Thus, according to the invention, the adduct formation is carried out in two stages under different pressures, the pressure of the second stage being lower than that of the first stage.

Of importance for the carrying out of the process according to the invention is the use of a solvent whose boiling point is so low that when the pressure is reduced in the second step the boiling point is exceeded. in the majority of cases the solvent will be an oil solvent. Thus, we have found that the adduct agglomerate includes an appreciable amount of the solvent, together with urea; the solvent content represents approximately one-quarter of the amount used. The reduction of pressure momentarily evaporates this solvent and breaks up the agglomerate, the unused urea is liberated and, at the same time, forms new adduct.

The difierence between the two pressure stages, and not the absolute degree of the pressures themselves, is decisive for the invention. Thus, it is possible, in the first step, to work at a pressure of one atmosphere and in the second step to work under vacuum or in the first step to use a pressure of several atmospheres and then to reduce to atmosphere pressure in the second step. In the same way, the pressure used in the second step can also amount to several atmospheres provided that the pressure used in the first step is greater.

If methylene chloride is used as a solvent then it is advantageous to carry out the adduct formation in the first step under normal pressure at the boiling point of methylene chloride (41 C.) and in the second step to reduce the pressure to about half an atmosphere.

It the methylene chloride is replaced by a solvent with a lower boiling point, for example difluorodichloromethane (B.P.-30 C.), then the first step must be carried out under pressure if the solvent to be used is to be added in a completely fluid condition. In the second step the pressure can be reduced to any desired lower pressure.

However, even solvents with a relatively high boiling point, such as cyclohexane (B.P. 81 C.) or dichloroethane (B.P. 83.7 C.), may be used. In order to bring the solvent included in the adduct to the evaporation point, a higher vacuum must, however, be used than is used in the case when methylene chloride is used.

As in specification No. 533,699 the use of urea solutions which contained 10 to 40% by weight of water referred to the solution possesses special advantages. After the adduct formation the mixture consists of only one fluid and one solid phase; the unused urea solution is completely absorbed into the adduct and does not appear as its own fluid phase. In this way the adduct possesses a fine-grained structure which allows it to be separated from the mixture by means of the simplest of separating devices. Any hydrocarbon oils containing n-paraffins may be used, regardless of their boiling range.

It is not necessary in all cases to use the solvent as an oil solvent. In the case of hydrocarbon oils with a low viscosity, such as kerosene, the dilution with a suitable oil solvent can be omitted, particularly if the oils in question contain very little n-paraflins. However, the suggested process is also applicable in this case if a low boiling point solvent for the urea is used together with water. A suitable solvent for the urea is, for example, methanol and water.

In the present process it is possible to use up the added urea almost completely, to shorten the adduct formation time and to save a considerable amount of stirring energy. Nevertheless, in this case the disadvantage arises that with the evaporation of the solvent the coarse adduct agglomerate crumbles to dust-fine powder. The separation of such a powder can no longer be carried out by means of a sieve.

However, it is possible to convert the dust-fine powder into a sievable agglomerate in a simple manner: it is only necessary to stir the mixture consisting of oil not capable of adduct formation and adduct dust in a subsequent step. The stir-ring times differ and vary between one and sixty minutes. On the other hand, small amounts of water, which may also contain urea, are added to the adduct-oil mixture. By brief stirring a fine granular material is formed which can be separated by means of a sieve.

The separated n-paraflin-urea adduct can, after separation, be decomposed into n-paraflins and urea by the methods described in specification No. 533,699.

What is claimed is:

1. A process for the separation of n-parafifins from hydrocarbon oils in the presence of an oil solvent by treating said oils with an aqueous solution of urea containing 10-40% by weight of water to form an n-paraffinurea adduct containing solvent and unused urea, characterised in that the formation of the n-parafiin-urea adduct is carried out in two stages under small differences of Patented Sept. 12, 1961 of the aforesaid oil solvent the boiling point of which is.

such that when the pressure is reduced in said second: stage the boiling point of said solvent is exceeded and evaporates, whereby the adductt' is physically broken up without decomposition of the adduct into its components, but liberates the unused urea which forms new adduot.

2; A process according to claim 1, wherein the solvent is a member selected from the group consisting of methylene chloride, difluorodichloromethane, cyclohexane and dichloroethane.

3. A process as set forth in. claim 1 and subsequently, in order to simplify the separation of the adduct, the grain size of said adduct is increased by stirring with an oil'not capable of adduct formation.

4; A process as set forth in claim 1 and subsequently, in order to simplify the separation of the adduct, the grain size of said adduot is increased by stirring the oil-adduct mixture with small amounts of water.

5. A process as setforth in claim 1 and subsequently, in order to simplify the separation of the adduct, the grain size of said adduct is increased by stirring the oiladduot mixture with small amounts of water which contains urea.

6'. The method of claim 1 in. which the solvent is methylene chloride, and the difference in pressure between the two stages is about 0.5 atmosphere.

References (Sited in the file of this patent UNITED STATES PATENTS 2,560,193 Shoemaker July 10, 1951 2,642,422 Gorin: June 16, 1953 2,658,887 Arnold etI-al Nov. 10, 1 9 53 2,723,220 Axe Nov. 8, 1955 2,763,637 McKayet al Sept. 18, 1 956 2,799,623 Leas July 16, 1957 2,800,466 Rosentein July 23, 1957 2,861,941 lancosek et a1 Nov. 25, 1958 2,907,708 Hoppe et al Oct. 6, 1959- 

1. A PROCESS FOR THE SEPARATION OF N-PARAFFINS FROM HYDROCARBON OILS IN THE PRESENCE OF AN OIL SOLVENT BY TREATING SAID OILS WITH AN AQUEOUS SOLUTION OF UREA CONTAINING 10-40% BY WEIGHT OF WATER TO FORM AN N-PARAFFINUREA ADDUCT CONTAINING SOLVENT AND UNUSED UREA, CHARACTERISED IN THAT THE FORMATION OF THE N-PARAFFIN-UREA ADDUCT IS CARRIED OUT IN TWO STAGES UNDER SMALL DIFFERENCES OF PRESSURE, THE PRESSURE OF THE SECOND STAGE BEING LOWER THAN THE PRESSURE OF THE FIRST STAGE, AND IN THE PRESENCE OF THE AFORESAID OIL SOLVENT THE BOILING POINT OF WHICH IS SUCH THAT WHEN THE PRESSURE IS REDUCED IN SAID SECOND STAGE THE BOILING POINT OF SAID SOLVENT IS EXCEEDED AND EVAPORATES, WHEREBY THE ADDUCT IS PHYSICALLY BROKEN UP WITHOUT DECOMPOSITION OF THE ADDUCT INTO ITS COMPONENTS, BUT LIBERATES THE UNUSED UREA WHICH FORMS NEW ADDUCT. 